RFR: 8306040: HttpResponseInputStream.available() returns 1 on empty stream [v2]

[Vyom Tewari]

> Please review the code change for [JDK-8306040](https://bugs.openjdk.org/browse/JDK-8306040). In the overridden "available" method of "HttpResponseInputStream" we are returning 1 after exploring all the code path.

Vyom Tewari has updated the pull request incrementally with one additional commit since the last revision:

  converted the test to junit and removed the one assert

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Changes:
  - all: https://git.openjdk.org/jdk/pull/14810/files
  - new: https://git.openjdk.org/jdk/pull/14810/files/5e6cb9ce..a4a6eaff

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=14810&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=14810&range=00-01

  Stats: 13 lines in 1 file changed: 2 ins; 4 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/14810.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14810/head:pull/14810

PR: https://git.openjdk.org/jdk/pull/14810